What is synovial osteochondromatosis?

Synovial Osteochondromatosis

Synovial osteochondromatosis is a rare, benign condition characterized by the formation of multiple cartilaginous or osteocartilaginous nodules within the synovial membrane of joints, resulting in loose bodies that can cause pain, swelling, and limited joint mobility.

Definition and Pathophysiology

Synovial osteochondromatosis (also called synovial chondromatosis) is a benign neoplastic condition that involves:

• Proliferation of chondrocytes in the synovial membrane
• Formation of cartilaginous nodules that may detach and become loose bodies within the joint space
• Potential calcification or ossification of these nodules over time

The condition is classified into two types:

1. Primary synovial osteochondromatosis: Results from metaplastic transformation of the synovial membrane with no underlying joint pathology 1
2. Secondary synovial osteochondromatosis: Develops as a consequence of pre-existing joint disease such as osteoarthritis, where fragments from damaged articular cartilage or osteophytes form loose bodies 2

Epidemiology

• Most commonly affects large joints, particularly the knee, followed by hip, elbow, and ankle 3
• Rarely affects smaller joints such as the temporomandibular joint 3
• Can occur at any age but typically presents in adults between 30-50 years
• More common in males than females

Clinical Presentation

Patients with synovial osteochondromatosis typically present with:

• Joint pain that worsens with activity
• Joint swelling due to effusion
• Limited range of motion
• Locking or catching sensations
• Crepitus during joint movement
• Symptoms may develop gradually over months to years 1, 4

Diagnosis

Diagnosis involves a combination of:

Clinical Evaluation

• History of joint pain, swelling, and mechanical symptoms
• Physical examination revealing joint effusion, limited range of motion, and palpable loose bodies in some cases

Imaging Studies

• Plain radiographs: May show multiple calcified or ossified loose bodies within the joint space, though early disease may not be visible 5, 1
• Ultrasound: Highly sensitive and specific for detecting joint effusions and loose bodies 5, 6
• MRI: Superior for detecting non-calcified loose bodies, synovial proliferation, and cartilage damage 6, 1

Histopathological Examination

• Confirmatory for diagnosis
• Shows cartilaginous nodules with varying degrees of calcification or ossification 1

Differential Diagnosis

• Osteoarthritis
• Rheumatoid arthritis
• Pigmented villonodular synovitis
• Synovial hemangioma
• Synovial sarcoma
• Chondrosarcoma (rare malignant transformation)

Treatment

Treatment options depend on the severity of symptoms and extent of disease:

Non-surgical Management

• Appropriate for mild, asymptomatic cases
• NSAIDs for pain control (ibuprofen 400-600mg TID or naproxen 500mg BID) 6
• Activity modification to avoid exacerbating movements 6
• Physical therapy to maintain joint mobility and strength

Surgical Management

• Arthroscopic removal of loose bodies: Preferred for most cases, especially when loose bodies are few and accessible 7
• Synovectomy: Indicated when there is extensive synovial involvement to reduce recurrence 1, 7
• Open surgery: May be necessary for extensive disease or when arthroscopy is not feasible 4
• Joint reconstruction or replacement: Reserved for cases with severe joint damage 1

Prognosis and Complications

• Generally good prognosis with appropriate treatment
• Recurrence rates of 3-23% have been reported, especially in cases without synovectomy
• Potential complications include:
  • Progressive joint damage leading to osteoarthritis if left untreated 1
  • Malignant transformation to chondrosarcoma (extremely rare, <1%) 1

Clinical Pearls and Pitfalls

Pearls

• Consider synovial osteochondromatosis in patients with persistent joint pain and mechanical symptoms not responding to conventional treatment
• MRI is the most sensitive imaging modality for early detection
• Arthroscopic treatment allows for both diagnosis and treatment with minimal invasiveness

Pitfalls

• Misdiagnosis is common due to nonspecific symptoms that mimic osteoarthritis 1, 3
• Delayed diagnosis can lead to progressive joint damage
• Failure to perform synovectomy may increase recurrence risk
• Overlooking the possibility of malignant transformation in long-standing cases

Monitoring and Follow-up

• Regular clinical follow-up to monitor for symptom recurrence
• Periodic imaging (radiographs or MRI) to assess for disease recurrence
• Long-term follow-up is recommended due to potential for recurrence and rare malignant transformation

Synovial osteochondromatosis should be considered in the differential diagnosis of persistent joint pain, particularly when mechanical symptoms are present and conventional treatments have failed. Early diagnosis and appropriate surgical intervention can significantly improve outcomes and prevent progressive joint damage.